Ohmic Heating Processing System Of Tofu Using Impedance Measurement

Tofu is a kind of healthy food people like it very much in Southeast Asia. Heating andcoagulation of soymilk are the most important two processes in tofu making. However, thecurrent methods of heating soymilk were unable to control the heating rate and temperatureprecisely, and the presence of temperature gradient caused the temperature of soymilk uneven,it could lead to the decline in the quality of tofu easily. While currently mainly rely onexperience to judge the degree of tofu coagulation, that could lead to tofu quality uneven thatproduced by different operators or different batches of the same operator. Aimed at theproblems of existing processing methods, designed a ohmic heating tofu processing systemthat use STC89C52RC MCU as controller, use thermocouple to measure temperature and usethe network analyzer chip to detect soymilk impedance in real time. The system is able tocontrol and measure the temperature of soymilk precisely, to determine the degree of tofucoagulation in real time, it improved the level of automation of tofu processing and improvedthe quality of tofu. The main work and conclusions of this study are as follows:(1) According to tofu making process and its requirements, the overall design of thesystem was determined, the system consists of the microcontroller, the heating tank withelectrode plate, temperature measurement module with thermocouple, switch module,impedance measurement module, LCD module, the input module with keys and serialcommunication module et al.(2) According to ohmic heating tofu processing system design, the hardware and softwareof the system has been designed. After comparing multiple solutions, chose K-typethermocouple and MAX6675chip to form temperature measurement module; chose relaysand optical coupler to form switch module; chose AD5933chip as impedance measurementmodule core component; chose LCD1602as display module core component. coded andtested software of the system.(3) Based on the finite element analysis, Used Comsol Multiphysics software to buildmathematical model, simulated the temperature distribution of cylindrical, cube, rectangularsix kinds of container in the heating process. by comparison, selected the optimal container.(4) Tested the system hardware, debugged the software and tested overall system. Theresults showed that the system is working properly. the temperature measurement error is ±1℃, the impedance measurement error is±1at low frequency, almost zero at highfrequencies; Impedance changes can be used to determine the end of coagulation of soymilkat10kHz.